Position and anchoring system for off-shore drilling platform

ABSTRACT

A monopad drilling structure in which the bottom of the structure is a flat surface resting on the ocean floor. A submerged cellar structure is emplaced over the drill site. Cables extend from the deck of the drilling platform through a moon pool extending through the bottom wall of the base. The cables extend radially outwardly from the opening and connect to the emplaced cellar structure. Controlling tension on the cables permits the platform to be moved laterally in relation to the cellar structure to move the moon pool directly over selected drilling locations within the confines of the cellar structure.

United States Patent [191 Schirtzinger Mar. 18, 1975 POSITION AND ANCHORING SYSTEM FOR OFF -SHORE DRILLING PLATFORM [75] Inventor: Joseph F. Schirtzinger, Pasadena,

Calif.

[73] Assignee: Sea-Log Corporation, Pasadena,

Calif.

[22] Filed: Apr. 8, 1974 21 Appl. No.: 459,030

8/1970 Vilain ..6l/46.5 2/1974 DeChassy l75/9 [57] ABSTRACT A monopad drilling structure in which the bottom of the structure is a flat surface resting on the ocean floor. A submerged cellar structure is emplaced over the drill site. Cables extend from the deck of the drilling platform through a moon pool extending through the bottom wall of the base. The cables extend radially outwardly from the opening and connect to the emplaced cellar structure. Controlling tension on the cables permits the platform to be moved laterally in relation to the cellar structure to move the moon pool directly over selected drilling locations within the confines of the cellar structure.

4 Claims, 5 Drawing Figures POSITION AND ANCHORING SYSTEM FOR OFF-SHORE DRILLING PLATFORM FIELD OF THE INVENTION This invention relates to off-shore drilling platforms, and more particularly, is concerned with lateral movement and anchoring of the drilling platform over a plurality of closely spaced drilling locations.

BACKGROUND OF THE INVENTION Various types of off-shore drilling platforms have been developed including permanent platforms, jackup and semi-submersible platforms. The permanent platform allows for drilling of multiple wells within the area defined by the supporting legs. Similarly, the jackup platform, when positioned, permits drilling of multiple wells within the area defined by the supporting structure. Semi-submersibles are anchored by cables and can be shifted more easily from drill site to drill site.

When operating in ice-covered waters, a monopod drilling platform having a single supporting column has proved advantageous, since it reduces the crosssectional area required at the surface which must be cleared of ice and also provides better protection of the drill string from surface ice. However, the monopod structure, in which the drill string passes through a central opening or moon pool extending to the base of the structure, requires some shifting of the structure laterally to permit multiple wells to be drilled at one location.

SUMMARY OF THE INVENTION The present invention provides an arrangement which anchors the platform securely in place on the ocean floor and yet permits the platform to be shifted laterally by small increments to move the center of the platform directly over any selected one ofa plurality of different well locations. This is achieved by providing a permanently emplaced structure or cellar on the ocean floor having a bottom wall large enough to cover a large number of well locations. The cellar has surrounding side walls extending upwardly to the level of the ocean floor.

A monopod drilling platform includes a lower hull which is submerged below the surface, the lower hull having a flat bottom surface slidably engaging the top of the cellar sidewalls and the surrounding ocean floor, the monopod drilling platform further including a deck positioned above the surface and a column supporting the deck on the submerged hull, with casing means extending from the bottom of the hull up the column to the deck. Cables extend from the deck through the casing into the cellar, the cables radiating from the lower end of the casing outwardly to the sidewalls of the cellar. By controlling tension on the cables, the platform can be pulled laterally relative to the cellar in any direction to position the platform at any selected drilling location within the boundaries of the cellar.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the invention, reference should be made to the accompanying drawings, wherein:

FIG. 1 is an elevational view of the drilling platform incorporating the features of the present invention;

FIG. 2 is a top view of the emplaced cellar structure;

FIG. 3 is a partial sectional view of the platform and cellar structure;

FIG. 4 is a top view of a cellar with an alternative cable arrangement; and

FIG. 5 is a partial cross-sectional view showing the cable control for the alternative embodiment of FIG. 4.

DETAILED DESCRIPTION Referring to FIG. 1, the numeral 10 indicates generally a monopod type drilling platform having a lower submerged hull 12, a vertical supporting column 14, and upper hull 16. The upper hull 16 includes a drilling deck 18 on which is supported a conventional drilling derrick 20. The drilling takes place through an open shaft or moon pool 22 extending from the drilling deck 18 down through the bottom 13 of the lower hull 12. The moon pool provides access to the substrata by the drilling rig.

The bottom 13 of the lower hull 12 is designed to rest on the ocean floor after proper site preparation, as described in copending application Ser. No. 458986, filed Apr. 18, 1974, entitled Method and Apparatus for Supporting a Drilling Platform on the Ocean Floor and assigned to the same assignee as the present application. Site preparation includes an excavating and levcling process of the ocean floor to provide a suitable supporting surface on which the lower hull rests. In addition, a cellar structure 24 is implanted in the ocean floor at the drilling site, the top of the cellar being made substantially flush with the leveled area.

Referring to FIGS. 2 and 3, the cellar 24 includes a cylindrical sidewall 26 and flat bottom wall 28. The cellar is preferably cast from concrete with the relatively thick sidewalls terminating in a flat annular top surface 30. A pipe manifold 31 is provided for connection of producing wells as they are drilled to an oil gathering point. the bottom 13 of the lower hull l2 rests in part on the surface 30, as shown in FIG. 3. The moon pool shaft 22 extending through the bottom of the lower hull is substantially smaller in diameter than the interior of the cellar 24.

In order to drill a number of wells at a plurality of well locations within the perimeter of the cellar, it is therefore necessary to shift the position of the moon pool relative to the cellar. According to one embodiment of the present invention, this is accomplished by running a single cable 32 from a winch on the drilling deck 18 down through the moon pool and attaching the cable to the cellar. For this purpose, a plurality of cable attaching lugs or positioned pad eyes 36 are provided around the interior of the cellar sidewall 26. The pad eyes 36 are located at points corresponding to the rows and columns of the well location matrix. The lower end of the moon pool shaft 22 is provided with a rounded lip 38 extending around the circumference of the opening into the interior of the cellar for the cable to ride over smoothly. Rollers or hawse pipes could also be used as suitable cable guides.

In order to move the center of the moon pool from one well location to the next, the cable 32 is attached to corresponding row or column pad eyes. By applying tension to the cable from the winch on the drilling deck, the entire platform can be moved laterally toward the pad eye which anchors the cable. Without moving the anchor point of the cable, the drilling platform can be moved so that the moon pool can be centered over each of the well locations in a selected row or column. Then by moving the cable, the platform can be shifted to the next adjacent row or column and advanced from well location to well location. The end of the cable is provided with a suitable hook 37 so that a diver may detach and reattach the end of the cable to selected pad eyes.

The platform is normally held in place on the cellar by flooding ballast chambers. The chambers are partially deballasted by means of compressed air, or the like, to reduce the friction load on the bottom of the platform during the repositioning.

An alternative arrangement is shown in FIGS. 4 and 5 in which a plurality of calbes, for example 8, extend down through the moon pool shaft 22, then ends of the cables extending radially outwardly from the bottom of the moon pool shaft to the anchoring lugs or pad eyes 36 on the inside surface of the cellar 24. As hown in FIG. 5, each of the calbes passed up and out through the top end of the moon pool shaft 22 at the drilling deck 18. Each cable passes over a pulley guide 40 mounted on the deck cables, the top of the moon pool shaft, the guides 40 directing the cable to an associated winch 42. By utilizing the respective winches 42 to control the tension on the cables, the drilling platform can be moved relative to the cellar. In this way, shown moon pool can be positioned over cables passes drilling location within the limits of the sidewalls of the cellar.

What is claimed is:

l. A drilling structure for drilling into the ocean floor from above the ocean surface, comprising a cellar having a bottom wall and sidewalls, the cellar being imbedded in the ocean floor and open at the top, a monopod drilling platform including a lower hull submerged below the surface, the lower hull having a flat bottom jacent the top of the column and a cable extending from the winch down through the passage and laterally from the bottom of the passage to the sidewalls of the cellar for moving the hull relative to the cellar by tension applied to the cable by the winch.

2. Apparatus of claim 1 wherein the cellar includes a plurality of anchor means spaced around the inside perimeter of the sidewalls to which the cable can be attached.

3. Apparatus of claim 1 including additional winches and associated cables extending through the passage from the deck to respective ones of the anchor means, each cable moving the hull in a different direction relative to the cellar.

4. The method of anchoring and positioning a drilling platform in ocean waters comprising emplacing an open cellar structure into the open floor, lowering the supporting bottom of the platform onto the top of the cellar structure, connecting one or more cables to the inside perimeter of the cellar structure from the center of the platform bottom, selectively applying tension to one or more of the cables from the platform to pull the center of the platform bottom in any lateral direction relative to the cellar structure.

UNITED STATES PATENT OFFICE QERTIFICATE OF CORRECTION PATENT NO. 3,871,184

DATED March 18, 1975 INVENTOR(S) 1 JOSEPH F. SCHIRTZINGER it is certified that error appears in the ab0ve-identitied patent and that said Letters Patent are hereby corrected as shown beiow:

In the Abstract, line 1, "monopad" should read monopod Column 3, line 13, "calbes" should read cables line 14, "then" should read the line 17, "hown" should read shown; line 18, "calbes" should read cables line 21, "cables" should read adjacent line 25, "shown" should read the line 26, "cables passes" should read any selected Signed and Scaled this nineree fl; D 3) Of August 1975 [SEAL] A ttes I:

RUTH C. MASON C. MARSHALL DANN Arresting ()jfirer ('mnmissimu'r uj'Palems and Trademurki 

1. A drilling structure for drilling into the ocean floor from above the ocean surface, comprising a cellar having a bottom wall and sidewalls, the cellar being imbedded in the ocean floor and open at the top, a monopod drilling platform including a lower hull submerged below the surface, the lower hull having a flat bottom surface slidably engaging the top of the cellar sidewalls, a drilling platform positioned above the surface, a column supporting the platform on the submerged hull, and casing means extending from the bottom of the hull up through the column to the drilling platform, the casing means forming an open vertical passage extending from the drilling deck to the cellar, the passage being substantially smaller in cross-section than the bottom of the cellar, and means including a winch mounted adjacent the top of the column and a cable extending from the winch down through the passage and laterally from the bottom of the passage to the sidewalls of the cellar for moving the hull relative to the cellar by tension applied to the cable by the winch.
 2. Apparatus of claim 1 wherein the cellar includes a plurality of anchor means spaced around the inside perimeter of the sidewalls to which the cable can be attached.
 3. Apparatus of claim 1 including additional winches and associated cables extending through the passage from the deck to respective ones of the anchor means, each cable moving the hull in a different direction relative to the cellar.
 4. The method of anchoring and positioning a drilling platform in ocean waters comprising emplacing an open cellar structure into the open floor, lowering the supporting bottom of the platform onto the top of the cellar structure, connecting one or more cables to the inside perimeter of the cellar structure from the center of the platform bottom, selectively applying tension to one or more of the cables from the platform to pull the center of the platform bottom in any lateral direction relative to the cellar structure. 